1. Field of the Invention
The present invention relates to a semiconductor laser element, and particularly, to a semiconductor laser element used as a light source for an information recording apparatus.
2. Description of the Related Art
A recording density in an optical disk for information recording has been increasingly raised because of development in digital information technology, and a high power capability has been simultaneously required in a semiconductor laser element, which is a light source for an information recording apparatus, because of improvement on an information recording speed onto an optical disk. It is unpreferable, however, to cause nonlinearity between a current and an optical output, such as a kink, in usage of the semiconductor laser element, and it is required to provide a semiconductor laser element that has no kink in high power state, in other words with a high kink level.
In order to improve a recording speed, a semiconductor laser element is effective that has a lens system guiding light from a semiconductor laser element to an optical disk and a low aspect characteristic (a ratio of a vertical spread angle FFPy to a horizontal spread angle FFPx, FFPy/FFPx is small), with which a high optical coupling efficiency can be obtained.
In such a way, it is necessary to use a semiconductor laser element with a high kink level and a low aspect ratio in order to improve a recording density.
Japanese Non-examined Patent Publication No. 2-178988 is referred herein.
There have been available the two methods to obtain a low aspect ratio: one method in which a small FFPy is adopted and the other in which a large FFPx is adopted, whereas problems have been arisen in both methods such that a temperature characteristic is degraded with a smaller FFPy adopted, while with a larger FFPx adopted, a kink level is lowered.
Therefore, there has been conventionally difficulty in fabricating a high output laser with a low aspect.
For example, if an FFPx is made larger in order to obtain a low aspect, light in a horizontal plane is required to be confined at a higher degree, wherein with confinement of light at a higher degree, inhomogeneity in carrier injection arises due to spatial hole burning, leading to generation of a kink.